1. Field of the Invention
The present invention relates to reflector plates for a reflective liquid crystal display and methods for fabricating the same, in particular to a method for fabricating reflector plates that can prevent light reflections from the exposure stage during the formation of undulating resin outgrowth, in order to avoid abnormal patterns occurring on the reflective surface, and furthermore the present invention can also shorten the exposure time and increase production yield.
2. Description of Related Arts
Reflective liquid crystal displays in general employ an external light source to illuminate display images. This new type of reflective display can effectively reduce the need of using a back light source and can achieve considerable saving on power consumption, making it suitable for portable applications.
Reflective displays in general have a reflector plate on the display panel, replacing the conventional back-light portion. These reflector plates can be further classified into a full reflective type and a semi-transmissive type. The reflective type reflector plate is usually equipped with a front-light module which is used to supplement external light for the necessary illumination on a liquid crystal display. The semi-transmissive type reflector plate, like a half-mirror, is able to receive light from a back-light module in supplement of external light when the ambient light is insufficient. However, display devices having either the reflective type or the semi-transmissive type reflector plate do not need the front-light or back-light illumination in the normal conditions, so their power consumption can be reduced. As mentioned earlier, the reflective display having a reflective type reflector plate is usually equipped with a front-light module. When the external light is insufficient, the display device can switch to the front-light module to supplement the ambient light. However, the above-mentioned reflective light technology has the shortcoming of noise signals and this is yet to be solved. As a result, the semi-transmissive type reflector plate is more favored by users. The semi-transmissive type reflector plate is able to use a back light to supplement the ambient light. This is implemented by creation of an undulating resin outgrowth on the reflective surface of the reflector plate.
FIG. 7 shows the steps for fabricating a semi-transmissive type reflector plate. A glass substrate (70) is prepared with thin film transistors built on top; and, a layer of transparent electrical conductor such as indium-tin-oxide (ITO) is deposited over the surface. Since the glass substrate (70) has thin film transistors formed in advance of the transparent electrodes, a pixel region is formed in between the glass substrate (70) and the transparent electrodes (71) with a gate insulating layer (701) and a protection layer (702).
The transparent electrodes (71) are formed by spin coating a layer polymer resin on the surface to form a photo-resist layer (72); then the photo-resist layer is exposed to light in a lithography process to remove photo-resist in areas other than the pattern areas to create a photomask as shown in FIG. 7b; then a metal layer as shown in FIG. 7c, is deposited on the surface to create a reflective film (73); the metal deposits in the non-pattern areas are removed after photo-etching to form a light transmitting region (74), thus completing the formation of a reflective type reflector plate with undulating resin outgrowth.
The reflective film (73) can be a single layer or multiple layers of film. In the case of a 3-layer film, the materials used in different layers are molybdenum alloy (Mo), aluminum (Al), and molybdenum alloy (Mo) in that order.
FIGS. 8a˜c shows the process of fabricating a reflective type reflector plate, in which the basic steps are similar to those used for a semi-transmissive type reflector plate, except that the step to create the light-transmitting region is not necessary for the reflective type reflector plate.
In the fabrication of the reflective type reflector plate mentioned above, it is necessary to point out that the process for fabricating the undulating resin outgrowth over the reflective surface will significantly affect the yield rate and the defect rate in the production of these reflector plates.
In detailed analysis of the fabrication process, the glass substrate (70) is placed on the exposure stage, and the photomask is precision aligned and fixed over the light projection areas of the exposure stage, a vacuum pad is then adhered to the bottom of the glass substrate (70) for firming the substrate, and the photo-resist layer is spin coated on the surface of the glass substrate (70) and exposed under light. In the process, the vacuum pad and the protrusion pins will cause light reflection from the exposure stage, leading to some undesired pattern marks on the surface due to uneven exposure of the photo-resist layer. The pattern marks still exist in a subsequent fabrication process of the reflective film (73). The pattern marks reflecting the shapes of the vacuum pad and the protrusion pins will be developed on the reflective film (73), thus seriously affecting the yield in the production of the reflector plates.
The problem of reflections from the exposure stage which will affect the yield rate of reflector plate output will have to be corrected.